1. Field of the Invention
The present invention relates to a positive resist composition and a pattern forming method, more specifically, a pattern forming method for use in the production process of a semiconductor such as IC, in the production of a circuit substrate of liquid crystal, thermal head or the like, or in other photofabrication processes, in particular, a pattern forming method by KrF or ArF exposure using a chemical amplification resist such as positive resist,
2. Description of the Related Art
The chemical amplification resist composition is a pattern forming material for forming a pattern on a substrate by producing an acid in the exposed area upon irradiation with actinic rays or radiation such as far ultraviolet light and through a reaction using this acid as the catalyst, changing the solubility in a developer between the portion irradiated with actinic rays or radiation and the non-irradiated portion.
With recent miniaturization of the circuit pattern of a semiconductor device, a lithography technique using an ArF excimer laser (193 nm) as the exposure light source is fully in progress and in order to cope with higher miniaturization, an immersion exposure technique of filling a high refractive index liquid (hereinafter sometimes referred to as an “immersion liquid”) between a projection lens and a sample is being applied to the mass production of a semiconductor device. Recent progress of the immersion exposure technique is reported, for example, in SPIE Proc., 4688, 11 (2002) and International Publication No. WO2004-077158, pamphlet.
However, even by employing this immersion exposure technique using an ArF excimer laser as the exposure light source, pattern formation of a 32 nm-generation semi-conductor device is considered to be impossible because of insufficient resolving power. For this reason, a method employing a special pattern forming method using an exposure machine having a projection lens with NA of 1.2 to 1.35 is attracting attention.
Several methods have been proposed for this special pattern forming method, and one of these methods is a double exposure process.
The double exposure process is a process of applying exposure twice on the same photoresist film, where the pattern in the exposure field is divided into two pattern groups and the exposure is preformed in twice for respective divided pattern groups.
JP-A-2002-75857 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) indicates that it is indispensable in this method to have, like a two-photon absorption resist, a property of the photosensitivity or solubility in a developer being changed in proportion to the square of exposure intensity, but a resist having such a property has not been developed yet.
Under such a circumstance, a resist composition assured of high resolving power and responsive also to a double exposure process is keenly demanded.